The essential constituent parts of an eccentric screw pump are the stator, the rotor, which runs therein, and the drive for the rotor. The rotor has the configuration of a screw with one or more turns and rotates in the bore of the stator, which likewise has a helical configuration, the number of turns of the bore of the stator being higher than the number of turns of the screw of the rotor.
In order to achieve the necessary sealing between the stator and rotor, the stator is provided with an elastomeric lining against which the rotor butts in a sealed manner. Sickle-shaped or banana-shaped chambers are produced between the rotor and the stator, and these chambers move from the suction side to the pressure side during operation of the rotor. The medium is delivered in these chambers.
Eccentric screw pumps are suitable for transporting viscous media under high pressure and for delivering media with solid particles. Furthermore, this design principle may also be used as a motor if the medium is pressed into the arrangement under high pressure, as a result of which the rotor is made to revolve in the stator. Applications of this are constituted by so-called underground drilling motors.
Functioning, results in both the stator and the rotor being wearing parts, which need to be exchanged regularly. This requires dismantling that, naturally, should take place as straightforwardly as possible, in particular when large pumps or motors are involved.
As far as the stator is concerned, two different types of design are known. In the case of one type of design, the lining is located in a smoothly cylindrical tube, the helical contour being restricted exclusively to the elastomeric lining. The elastomeric lining is thus more compliant in the region of the thread crests than in the region of the thread troughs. Pumps of this type make it possible to produce a relatively low pressure for each stage because the relatively pronounced compliance in the region of the thread crest limits the maximum pressure.
In the case of the other type of construction, the casing is likewise, once again, a tube that nevertheless, for its part, is deformed helically. The lining has a constant wall thickness at all points both in the longitudinal direction and in the circumferential direction. This makes it possible to achieve very high pressures in comparative terms.
While in the case of the embodiment with a cylindrical casing the connection to the other pump-housing parts is comparatively straightforward, it is problematic in the case of the helically deformed tube. In the case of the simplest embodiment with a two-turn screw, the cross-section of the tube has the configuration of an oval similar to a racetrack, the available end surface of the casing being comparatively narrow. It is correspondingly difficult to achieve the sealing and the fastening on the pump housing.
Furthermore, the helically configured casing is sensitive to deformation at the ends on account of the pressure built up in the interior. While, in the central region of the stator, the adjacent stator regions help to stabilize the shape of said central region, free edges occur at the ends, which can easily result in deformation on the pressure side and thus in a loss of pressure, which limits the maximum possible pressure of the pump.
Taking this as the departure point, the object of the invention is to provide an eccentric screw pump or motor of which the stator has a helically configured casing and which can be easily connected to the rest of the housing parts, the ends thereof, without any significant increase in the axial length, being protected in an effective manner against changes in configuration as a result of the static pressure of the medium.
This object is achieved according to the invention by an eccentric screw pump or an eccentric screw motor having the features of claim 1.
The end ring, of which the through-opening continues the helical configuration of the interior of the stator casing, helps to achieve two things:
The complicated geometry of the stator end is transferred into a geometry which can easily be connected to the parts of the pump housing. This simultaneously provides a sufficiently large surface for accommodating seals. The surfaces are large enough in order for crushing of the seal to be prevented in an effective manner.
Furthermore, without the construction of the stator being extended in any way, the end ring allows the stator end to be secured against expansion, in particular the rectilinearly running section of the casing cross section decreasing [sic] sensitive to deformation. These regions are stabilized by the end ring and thus obtain a similar strength to that in the central region of the stator.
It is possible, for example, for the end ring to be designed as a flange plate which can be screwed to a correspondingly [sic] flange on the pump head or on the connection head, the two lying flat one upon the other.
That embodiment of the end ring which differs from the above in principle has a narrow ring, with a circular outer contour, which can be plugged into a corresponding stepped bore, designed as a seat, on the pump head or on the connection head. Here too, correspondingly large sealing surfaces are produced. The casing of the stator we [sic] particularly reinforced in the sections of the cross-sectional profile which have a low level of curvature, because, in these regions, the end ring, in order to follow the cylindrical outer configuration, has a particularly large wall thickness and is flexurally rigid.
Two embodiments are possible, in principle, for connecting the end ring straightforwardly to the casing of the stator. In one case, the end ring has a through-passage opening which has a constant cross section, as seen over the length, the cross section essentially coinciding with the outer cross section of the casing in order that the end ring can be screwed onto the casing like a type of nut. In order to prevent the end ring from being screwed onto the casing to too great an extent, a shoulder is formed on the casing. The shoulder may be formed by material being applied at the location of the shoulder or by material being removed from the outer circumferential surface, starting from the end of the casing. The simplest way of removing the material is by stripping the outer surface of the casing over the length over which the end ring is to be screwed on. As a result, the outer contour is only changed at those points at which the casing has the greatest radial extent. It goes without saying that the inner contour of the opening in the end ring is adapted to this changed outer contour of the casing, in order that only a very small installation gap is produced between the through-passage opening and the outer circumferential surface of the casing. This embodiment, furthermore, has the advantage that the end ring obtains a usable wall thickness at its weakest point.
The other of the two abovementioned variants makes use of an end ring in the case of which the through-passage opening is configured as a stepped bore, with the result that a shoulder is produced in the end ring, said shoulder positioning itself against the end surface of the casing as the end ring is screwed on. In this case, the cross section of the one section corresponds to the stepped bore of the outer cross section of the casing, while that section of the stepped bore which has a small [sic] surface area constitutes a fairly precise continuation of the interior of the casing.
In all cases, it is ensured that the end surfaces of the end ring are positioned at right angles in relation to the axis of the casing.
The end ring, once placed in position, may be connected integrally to the casing in order to improve the stability further. This expediently takes place by the end surface of the casing being welded to the end ring. Welding exclusively on the outer side would likewise be conceivable, but would leave a gap on the inner side, which gap possibly takes effect in the event of loading and could damage the continuous lining.